Imaging lens including seven lenses of ++−++−− or ++−+++− refractive powers

Abstract

There is provided an imaging lens with excellent optical characteristics which satisfies demand of a low profile and a low F-number. An imaging lens comprises in order from an object side to an image side, a first lens with positive refractive power, a second lens with positive refractive power, a third lens with negative refractive power, a fourth lens with positive refractive power, a fifth lens with positive refractive power, a sixth lens, and a seventh lens with negative refractive power, wherein said first lens has an object-side surface being convex in a paraxial region, said second lens has an image-side surface being convex in a paraxial region, said third lens has an object-side surface being concave in a paraxial region, said fourth lens has an object-side surface being concave in a paraxial region, said sixth lens has an object-side surface being convex in a paraxial region, and said seventh lens has an image-side surface being concave in a paraxial region.

What is claimed is: 
     
       1. An imaging lens comprising, in order from an object side to an image side,
 a first lens with positive refractive power, 
 a second lens with positive refractive power, 
 a third lens with negative refractive power, 
 a fourth lens with positive refractive power, 
 a fifth lens with positive refractive power, 
 a sixth lens, and 
 a seventh lens with negative refractive power, 
 
       wherein said first lens has an object-side surface being convex in a paraxial region, said second lens has an image-side surface being convex in a paraxial region, said third lens has an object-side surface being concave in a paraxial region, said fourth lens has an object-side surface being concave in a paraxial region, said sixth lens has an object-side surface being convex in a paraxial region, and said seventh lens has an image-side surface being concave in a paraxial region. 
     
     
       2. The imaging lens according to  claim 1 , wherein an object-side surface of said seventh lens is convex in a paraxial region. 
     
     
       3. The imaging lens according to  claim 1 , wherein the following conditional expression (1) is satisfied:
   0.02<( D 6/| f 6|)×100<2.55  (1)
 
 where 
 D6: a thickness along the optical axis of the sixth lens, and 
 f6: a focal length of the sixth lens. 
 
     
     
       4. The imaging lens according to  claim 1 , wherein the following conditional expression (2) is satisfied:
   0.50< f 1/ f< 1.70  (2)
 
 where 
 f1: a focal length of the first lens, and 
 f: a focal length of the overall optical system of the imaging lens. 
 
     
     
       5. The imaging lens according to  claim 1 , wherein the following conditional expression (3) is satisfied:
   3.75< f 5/ f< 17.50  (3)
 
 where 
 f5: a focal length of the fifth lens, and 
 f: a focal length of the overall optical system of the imaging lens. 
 
     
     
       6. The imaging lens according to  claim 1 , wherein the following conditional expression (4) is satisfied:
   0.20<( f 1/| f 6|)×100<35.00  (4)
 
 where 
 f1: a focal length of the first lens, and 
 f6: a focal length of the sixth lens. 
 
     
     
       7. The imaging lens according to  claim 1 , wherein the following conditional expression (5) is satisfied:
   0.60< r 13/ f< 3.50  (5)
 
 where 
 r13: a paraxial curvature radius of an object-side surface of the seventh lens, and 
 f: a focal length of the overall optical system of the imaging lens.